function fn1() {
  var n = 4399;
  function add() {
    n++;
    console.log(n);
  }
  return {
    n: n,
    add: add
  }
}

let obj1 = fn1();
let obj2 = fn1();
console.log(obj1);
console.log(obj2);
console.log(obj1 === obj2); // false

obj1.add();//4400
obj1.add();// 4401
obj2.add();// 4400
console.log(obj1.n); // 4399